The present invention relates to a self-focusing fiber array in which a number of self-focusing fibers are arrayed in a plurality of rows.
Generally, the self-focusing fiber is a transparent thin fiber whose cross section is round in shape and its refractive index n(r) at a distance r from the center of the cross section is represented by the following equation: ##EQU3## where n.sub.o represents the refractive index at the center of the cross section of the self-focusing fiber and a is a positive constant.
The self-focusing fiber has a function of image formation. When the self-focusing fiber is employed in the image formation apparatus of an electrophotographic copying apparatus or of a cathode ray tube apparatus, the self-focusing fiber is used in the form of a self-focusing fiber array in which a number of the self-focusing fibers having an equal length are arrayed in a row, with each end surface of the self-focusing fibers lined up.
The types of images formed by the self-focusing fiber vary, depending upon its length. Namely, by changing the length of the self-focusing fiber, images, which are equal, magnified, and reduced in size, can be selectively obtained and furthermore, erecting image, inverted image, real image and virtual image can also be obtained selectively. Therefore, the length of the self-focusing fiber determines the type of the formed image.
Japanese patent publications Nos. 37550/75 and 28058/72 disclose that length Z of the self-focusing fiber for forming equally magnified erecting images is described to be in the following range: ##EQU4## where m is a positive integer. However, when m is 2 or more under this condition, the self-focusing fiber cannot be used practically in view of its brightness, unevenness of the quantity of light, resolution, etc. Furthermore, in Japanese patent publication No. 10455/72, it is described that the length Z of the self-focusing fiber at the time an equally magnified erecting image is formed at the end surface of the self-focusing fiber is ##EQU5## where n is a positive integer. However, this condition is not practical since unevenness of the quantity of light is too great. In this image formation method in which images are formed at the end surface of the self-focusing fiber, the image formation end surface of the self-focusing fiber has to be brought into close contact with the surface of a photoconductor. In order to prevent the image formation end surface of the self-focusing fiber from being smeared, a design is made so as to retract the self-focusing fiber from the surface of photoconductor except during the exposure process.